U.S. patent number 7,346,286 [Application Number 11/155,827] was granted by the patent office on 2008-03-18 for method and apparatus for image forming effectively detecting deterioration of developer.
This patent grant is currently assigned to Ricoh Company, Ltd.. Invention is credited to Nobuo Iwata, Takayuki Koike, Eriko Maruyama, Junichi Matsumoto, Satoshi Muramatsu, Nobutaka Takeuchi.
United States Patent |
7,346,286 |
Matsumoto , et al. |
March 18, 2008 |
Method and apparatus for image forming effectively detecting
deterioration of developer
Abstract
A developer container includes a developer container configured
to contain a developer including a toner and a carrier, a developer
delivering mechanism configured to deliver the developer toward an
image bearing member of an image forming apparatus, and a detecting
mechanism configured to detect deterioration of the developer based
on a predetermined characteristic of the developer.
Inventors: |
Matsumoto; Junichi (Yokohama,
JP), Iwata; Nobuo (Sagamihara, JP),
Muramatsu; Satoshi (Tokyo, JP), Takeuchi;
Nobutaka (Yokohama, JP), Koike; Takayuki
(Yokohama, JP), Maruyama; Eriko (Sagamihara,
JP) |
Assignee: |
Ricoh Company, Ltd. (Tokyo,
JP)
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Family
ID: |
35045276 |
Appl.
No.: |
11/155,827 |
Filed: |
June 20, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060008281 A1 |
Jan 12, 2006 |
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Foreign Application Priority Data
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Jun 18, 2004 [JP] |
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2004-180565 |
Feb 24, 2005 [JP] |
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2005-049206 |
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Current U.S.
Class: |
399/29;
399/259 |
Current CPC
Class: |
G03B
15/08 (20130101); G03G 15/0848 (20130101) |
Current International
Class: |
G03G
15/08 (20060101) |
Field of
Search: |
;399/27,29,30,58,60,61,62,63,64,258,259 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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53-049439 |
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59-100471 |
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02-093568 |
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04-080777 |
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JP |
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04-344674 |
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Dec 1992 |
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JP |
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05-307327 |
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JP |
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06-348134 |
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08-036297 |
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08-211723 |
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09-251235 |
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09-269644 |
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09-297462 |
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11-212346 |
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2000-075629 |
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2000-081787 |
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2000-105498 |
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2000-181161 |
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2001-183893 |
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JP |
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2001-265101 |
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Sep 2001 |
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JP |
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2004-184698 |
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Jul 2004 |
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JP |
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Other References
US. Appl. No. 10/738,028, filed Dec. 18, 2003, Muramatsu et al.
cited by other .
U.S. Appl. No. 10/830,223, filed Apr. 23, 2004, Yanagisawa et al.
cited by other .
U.S. Appl. No. 11/045,293, filed Jan. 31, 2005, Muramatsu et al.
cited by other .
U.S. Appl. No. 11/516,659, filed Sep. 7, 2006, Iwata et al. cited
by other .
U.S. Appl. No. 11/748,090, filed May 14, 2007, Takeuchi et al.
cited by other .
U.S. Appl. No. 11/761,731, filed Jun. 12, 2007, Tanaka et al. cited
by other .
U.S. Appl. No. 11/751,163, filed May 21, 2007, Katoh et al. cited
by other.
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Primary Examiner: Brase; Sandra L.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
The invention claimed is:
1. A developing device, comprising: a developer container
configured to contain a developer including a toner and a carrier;
a developer delivering mechanism configured to deliver the
developer toward an image bearing member of an image forming
apparatus; and a detecting mechanism configured to detect
deterioration of the developer based on a predetermined
characteristic of the developer, wherein: the detecting mechanism
comprises a toner density sensor with a detecting portion
configured to obtain a toner density of the toner by detecting
magnetic permeability of the developer; and the detecting mechanism
detects the deterioration of the developer based on an output
waveform of the toner density obtained by the toner density
sensor.
2. The developing device according to claim 1, further comprising:
a removing member configured to remove the developer adhered on the
detecting portion of the toner density sensor, and wherein: the
toner density sensor detects the deterioration of the developer
based on the output waveform of the toner density that varies when
the removing member removes the developer from the detecting
portion of the toner density sensor.
3. The developing device according to claim 2, wherein: the toner
density sensor detects the deterioration of the developer based on
a first output waveform having a first slope formed between a first
peak value and a first bottom value thereof and a second output
waveform having a second slope formed between a second peak value
and a second bottom value thereof.
4. The developing device according to claim 2, wherein: the toner
density sensor detects the deterioration of the developer based on
a first output waveform having a first period of time between a
first peak value and a first bottom value thereof and a second
output waveform having a second period of time between a second
peak value and a second bottom value thereof.
5. The developing device according to claim 2, wherein: the toner
density sensor detects the deterioration of the developer based on
a first output waveform having a first output value thereof
obtained at a first predetermined point of time and a second output
waveform having a second output value thereof obtained after a
second predetermined period of time from the first predetermined
point of time.
6. The developing device according to claim 2, wherein: the toner
density sensor detects the deterioration of the developer based on
the output waveform of the toner density obtained when the
developer is fresh.
7. The developing device according to claim 2, wherein: the
developer delivering mechanism comprises a conveying screw
configured to convey the developer; and the removing member is
integrally mounted on the conveying screw.
8. The developing device according to claim 7, wherein: the
detecting portion of the toner density sensor is disposed at a
bottom portion of an inner wall of the developer container, in
which the removing member contacts with the developer contained in
the developer container.
9. The developing device according to claim 1, wherein: the
detecting mechanism performs a detecting operation under a
condition in which a constant toner density is maintained.
10. A developing device, comprising: a developer container
configured to contain a developer including a toner and a carrier;
a developer delivering mechanism configured to deliver the
developer toward an image bearing member of an image forming
apparatus; and a detecting mechanism configured to detect
deterioration of the developer based on a predetermined
characteristic of the developer, wherein: the developer delivering
mechanism comprises a developer carrying member configured to carry
the toner contained in the developer to the image bearing member;
the detecting mechanism comprises a developer amount sensor
configured to obtain an amount of the developer carried on a
surface of the developer carrying member; and the detecting
mechanism detects the deterioration of the developer based on the
detected amount of the developer.
11. The developing device according to claim 10, wherein: the
developer amount sensor detects the deterioration of the developer
based on a first amount of the developer obtained after a first
period of time from when the developer carrying member stops a
delivering operation of the developer and a second amount of the
developer obtained after a second period of time from when the
developer carrying member resumes the delivering operation of the
developer.
12. The developing device according to claim 10, wherein: the
developer amount sensor detects the deterioration of the developer
based on a first amount of the developer obtained prior to a
warm-up operation at a power-on of the image forming apparatus and
a second amount of the developer obtained in the warm-up operation
of the image forming apparatus.
13. The developing device according to claim 10, wherein: the
developer amount sensor detects the deterioration of the developer
based on a first amount of the developer obtained after a first
period of time from when the developer carrying member performs a
delivering operation of the developer and a second amount of the
developer obtained after a second period of time from when the
developer carrying member stops the delivering operation of the
developer.
14. The developing device according to claim 10, wherein: the
developer amount sensor detects the deterioration of the developer
based on the amount of the developer obtained after a predetermined
number of printouts are output.
15. The developing device according to claim 10, wherein: the
developer amount sensor detects the deterioration of the developer
based on the amount of the developer obtained after a predetermined
period of time from when the developer carrying member performs a
delivering operation of the developer.
16. The developing device according to claim 10, wherein: the
developer amount sensor detects the deterioration of the developer
vased on the amount of the developer obtained by performing a
plurality of detections in combination.
17. The developing deice according to claim 10, wherein: the
developer amount sensor includes a sensor having a same structure
as an image density sensor included in the image forming
apparatus.
18. The developing device according to claim 10, further comprising
a regulating memmber configure to regulate an amount of the
developer carried by the developer carryng member, and wherein: the
developer amount sensor is disposed downstream of the regulating
member in a derection to which the developer is delivered by the
developer carrying member.
19. The developing device according to claim 10, wherein: the
developer carrying member includes a surface having a material
harder than the developer.
20. The developing device accorfing to claim 10, wherein: the
developer amount sensor detects the deterioration of the developer
in accordance with a relationship between a developer conveying
aperation of the developer carrying member and a surface roughness
of the developer carrying member and a relationship between the
surface roughness and the amount of the developer obtained by the
develaper amount sensor.
21. A developing device, comprising: a developer container
configured to containg a developer including a toner and a carrier;
a developer delivering mechanism configured to deliver the
developer toward an image bearing member of an image forming
apparatus; and a detecting mechanism configured to detect
deterioration of the developer based on a predetermined
characteristic of the developer, wherein: the detecting mechanism
comprises: a developer deterioration sensor configured to obtain a
degree of deterioration of the developer; and a toner deterioration
sensor configured to obtain a degree of deterioration of the toner
included in the developer, and wherein: the deterioration of the
developer is detected based on the degree of the deterioration of
the developer and the degree of deterioration of the toner.
22. The developing device according to claim 21, wherein: the
detecting mechanism detects the deterioration of the toner based on
a fluidity of the developer delivered by the developer delivering
mechanism.
23. The developing device according to claim 21, wherein: the
developer deterioration sensor includes a background contamination
sensor configured to obtain an amount of a contamination on a
surface of the image bearing member.
24. The developing device according to claim 23, wherein: the
background contamination sensor includes a reflection density
sensor.
25. The developing device according to claim 21, wherein: the
developer deterioration sensor includes a toner scattering sensor
configured to obtain an amount of the toner scattering out of the
developing device.
26. The developing device according to claim 25, wherein: the toner
scattering sensor includes an optical sensor comprising: a light
emitting portion configured to emit a light beam; and a light
receiving portion configured to receive the light beam emitted by
the light emitting portion, and thereafter reflected by the toner
scattering out of the developing device.
27. A developing device, comprising: a developer container
configured to contain a developer including a toner and a carrier;
a developer delivering mechanism configured to deliver the
developer toward an image bearing member of an image forming
apparatus; a detecting mechanism configured to detect deterioration
of the developer based on a predetermined characteristic of the
developer; a supplying mechanism configured to supply fresh
developer including one of fresh carrier and a mixture of fresh
toner and the fresh carrier to the developer container when the
deterioration of the developer is detected; and a collecting
mechanism configured to collect excess developer, wherein: a user
is allowed to control a supplying operation performed by the
supplying mechanism.
28. A developing device, comprising: a developer container
configured to contain a developer including a toner and a carrier;
a developer delivering mechanism configured to deliver the
developer toward an image bearing member of an image forming
apparatus; a detecting mechanism configured to detect deterioration
of the developer based on a predetermined characteristic of the
developer; a supplying mechanism configured to supply fresh
developer including one of fresh carrier and a mixture of fresh
toner and the fresh carrier to the developer container when the
deterioration of the developer is detected; and a collecting
mechanism configured to collect excess developer, wherein; the
supplying mechanism stops the supplying operation to issue a
warning to the user when the deterioration of the developer is
detected after the supplying mechanism repeatedly supplies the
fresh developer for a predetermined number of times.
29. A developing device, comprising: means for containing a
developer including a toner and a carrier; means for delivering the
developer toward an image bearing member of an image forming
apparatus; and means for detecting deterioration of the developer
based on a predetermined characteristic of the developer, wherein:
the means for detecting comprises means for obtaining a toner
density of the toner with a detecting portion by detecting magnetic
permeability of the developer; and the means for detecting detects
the deterioration of the developer based on an output waveform of
the obtained toner density.
30. The developing device according to claim 29, further
comprising: means for removing the developer adhered on the
detecting portion of the means for obtaining, and wherein: the
means for obtaining detects the deterioration of the developer
based on a characteristic of the output waveform of the toner
density that varies when the means for removing removes the
developer from the detection portion of the means for
obtaining.
31. The developing device according to claim 30, wherein: the means
for obtaining detects the deterioration of the developer based on
the output waveform obtained when the developer is fresh.
32. The developing device according to claim 29, wherein: the means
for detecting performs a detecting operation under a condition in
which a constant toner density is maintained.
33. The developing device according to claim 29, further
comprising: means for supplying fresh developer including one of
fresh carrier and a mixture of fresh toner and the fresh carrier to
the means for containing when the deterioration of the developer is
detected; and means for collecting excess developer.
34. A developing device, comprising: means for containing a
developer including a toner and a carrier; means for delivering the
developer toward an image bearing member of an image forming
apparatus; and means for detecting deterioration of the developer
based on a predetermined characteristic of the developer, wherein:
the means for delivering comprises means for carrying the toner
contained in the developer to the image bearing member; the means
for detecting comprises means for obtaining an amount of the
developer carried by the means for carrying; and the means for
detecting detects the deterioration of the developer based on the
amount of the developer.
35. The developing device according to claim 34, wherein: the means
for obtaining detects the deterioration of the developer in
accordance with a relationship between a developer convenying
operation performed by the means for carrying and a surface
roughness of the means for carrying and a relationship between the
surface roughness and the amount of the developer obtained by the
means for obtaining.
36. A developing device, comprising: means for containing a
developer including a toner and a carrier; means for delivering the
developer toward an image bearing member of an image forming
apparatus; and means for detecting deterioration of the developer
based on a predetermined characteristic of the developer, wherein:
the means for detecting comprises: first means for obtaining a
degree of deterioration of the developer; and second means for
obtaining a degree of deterioration of the toner included in the
developer, and wherein: the deterioration of the developer is
detected based on the degree of the deterioration of the developer
and the degree of deterioration of the toner.
37. The developing device according to claim 36, wherein: the
second means for obtaining detects the deterioration of the toner
based on a fluidity of the developer delivered by the means for
delivering.
38. A method of detecting deterioration of developer, comprising:
filling a developer including a toner and a carrier in a developing
device; delivering the developer toward an image bearing member
disposed in a vicinity of the developing device; and detecting
deterioration of the developer based on a predetermined
characteristic of the developer, wherein: the detecting comprises:
removing the developer adhered on a detecting portion; obtaining a
toner density of the toner by magnetic permeability; and detecting
the deterioration of the developer based on an output waveform of
the toner density.
39. The method according to claim 38, further comprising: supplying
fresh developer including one of fresh carrier and a mixture of
fresh toner and the fresh carrier when the deterioration of the
developer is detected; and collecting excess developer.
40. A method of detecting deterioration of developer, comprising:
filling a developer including a toner and a carrier in a developing
device; delivering the developer toward an image bearing member
disposed in a vicinity of the developing device; and detecting
deterioration of the developer based on a predetermined
characteristic of the developer, wherein: the delivering comprises:
providing a developer carrying member; and delivering the toner
contained in the developer to the developer carrying member; and
the detecting comprises: obtaining an amount of the developer on a
surface of the developer carrying member; and detecting the
deterioration of the developer based on the amount of the
developer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present patent application claims priority under 35 U.S.C.
.sctn. 119 to Japanese patent applications No. 2004-180565 filed on
Jun. 18, 2004, and No. 2005-049206 filed on Feb. 24, 2005 in the
Japan Patent Office, the entire contents of each of which are
hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for image
forming, and particularly relates to a method and apparatus for
image forming capable of effectively detecting deterioration of
developer.
2. Description of the Background Art
An image forming apparatus such as a copier, facsimile machine,
printer, etc. generally includes an image bearing member such as a
photoconductive element, and a developing device. Some background
developing devices develop an electrostatic latent image formed on
a surface of the image bearing member with two-component developer
including toner and carrier.
When a developing device performs an image forming operation, the
toner may constantly be consumed while the carrier may remain in
the developing device. Even through fresh toner is supplied
accordingly, the fresh toner may not be sufficiently agitated or
mixed with the developer previously contained in the developing
device. Some amount of the fresh toner cannot contact with magnetic
carrier included in the developer in the above-described developing
device and cannot substantially be charged or may be charged to an
opposite polarity, causing problems such as image nonuniformity
including fogging and contamination due to toner scattering.
The developing device may include an agitating member to agitate
and mix the developer and the fresh toner, and uniformly distribute
the fresh toner. However, repeated abrasion and collision of the
toner and carrier in the developing device may cause deterioration
of carrier such as contamination of a carrier particle and peeling
of a coating layer of the carrier particle. This may gradually
decrease a charging ability of the carrier, resulting in a
substantial degradation of quality in an image.
The developer contained in a developer container of the developing
device may be replaced on some regular basis before the problem
related to image quality based on deterioration of carrier arises,
but large labor and cost may be needed for such a replacement of
the developer.
A trickle developing system may be employed to the developing
device to supply developer including carrier and toner mixed
therein or carrier and toner separately to a developer container of
the developing device. The trickle developing system may supply
fresh carrier as well as fresh toner, and discharge excess
developer having degraded charging ability, or deteriorated
developer, from the developer container to a collected developer
container so that the deteriorated developer can be replaced and
the degradation of the charging ability can be prevented.
The developing device with the trickle developing system supplies
the amount of carrier in a constant ratio to the amount of consumed
toner. However, a characteristic of carrier may significantly
change depending on conditions for use of the image forming
apparatus, generating a degradation of quality in an image when an
amount of fresh carrier supplied to the developing device is too
small to replace the deteriorated carrier, and resulting in a waste
of carrier when an amount of fresh carrier supplied to the
developing device is too large.
To prevent the degradation of charging ability, a small amount of
fresh carrier may be supplied to the developing device in
accordance with the frequency of the developing operations while
the compensation of toner consumed in the developing operation is
performed. This technique is proposed based on an idea that
deterioration of carrier may be proportional to a period of time
the developer container is operated or may be inversely
proportional to an amount of toner consumed in the developing
operation. The developing device may also detect the deterioration
of carrier electrically.
It is not easy to directly detect the deterioration of carrier
since a speed of deterioration of carrier depends on a temperature,
humidity, a number of outputs, frequency of operations, etc. of the
developer container. Because of frequent collision and abrasion
with the fresh toner and the carrier previously contained in the
developing device, some carriers allow the toner to adhere to the
carriers when a larger amount of toner is consumed.
A toner density sensor is used to detect the deterioration of
developer at a predetermined period of time after a beginning of
using the developer, but is not provided with a specific standard
to determine the deterioration of developer. Further, the decrease
of a toner density or the number of printouts cannot determine the
deterioration of developer. The determination of the deterioration
of developer based on the number of printouts may ignore variations
of the deterioration of carrier caused by differences of an image
area ratio or an image pattern.
It is desirable that the developer may be supplied not based on a
period of use time of the developer but based on a result obtained
by the detection of the deterioration of carrier. However, no
concrete mechanism of directly detecting the deterioration of
carrier with high accuracy has been proposed. From a view point of
cost reduction, previously proposed mechanisms may be more useful
to detect the deterioration than inventing a brand new one.
The developer can automatically be replaced when a condition of the
developer reaches a predetermined value, when the toner adheres to
a conductive roller contacting the developer, or when the condition
of the developer exceeds a predetermined electric value. However,
the above-described changes in characteristic values cannot show
whether toner or carrier causes the deterioration of developer.
Since a replacement of developer may be performed by discharging
the deteriorated carrier and supplying fresh carrier, a
deterioration level of the carrier needs to be detected based on
the entire characteristics of the developer.
A plurality of sensors including an optical sensor can be used to
measure respective characteristics of the developer, such as
magnetic permeability, toner density, an electric value, etc.
However, for example, it is not obvious at which part of an
apparatus the sensor measuring the electric value can be disposed.
As described above, even though a detecting mechanism is provided,
such detecting mechanism is not for detecting the deterioration of
developer based on the characteristics of the entire developer.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to eliminate
the above-described drawbacks.
Another object of the present invention is to provide a novel
developing device capable of effectively detecting deterioration of
developer.
Another object of the present invention is to provide a novel
method of detecting deterioration of developer.
Another object of the present invention is to provide a novel image
forming apparatus including a novel developing device capable of
effectively detecting deterioration of developer.
In one embodiment, a novel developing device includes a developer
container configured to contain a developer including a toner and a
carrier, a developer delivering mechanism configured to deliver the
developer toward an image bearing member of an image forming
apparatus, and a detecting mechanism configured to detect
deterioration of the developer based on a predetermined
characteristic of the developer.
The detecting mechanism may include a toner density sensor that has
a detecting portion and is configured to obtain a toner density of
the toner by magnetic permeability. The toner density sensor may
detect the deterioration of the developer based on an output
waveform of the toner density obtained by the toner density
sensor.
The novel developing device may further include a removing member
configured to remove the developer adhered on the detecting portion
of the toner density sensor.
The developer delivering mechanism may include a conveying screw
configured to convey the developer. The removing member may be
integrally mounted on the conveying screw.
The developer delivering mechanism may include a developer carrying
member configured to carry the toner contained in the developer to
the image bearing member, and the detecting mechanism may include a
developer amount sensor configured to obtain an amount of the
developer carried on a surface of the developer carrying member.
The developer amount sensor may detect the deterioration of the
developer based on the amount of the developer.
The novel developing device may further include a regulating member
configured to regulate an amount of the developer carried by the
developer carrying member. The developer amount sensor may be
disposed downstream of the regulating member in a direction to
which the developer is delivered by the developer carrying
member.
The detecting mechanism may include a developer deterioration
sensor configured to obtain a degree of deterioration of the
developer, and a toner deterioration sensor configured to obtain a
degree of deterioration of the toner included in the developer. The
deterioration of the developer may be detected based on the degree
of the deterioration of the developer and the degree of
deterioration of the toner.
The novel developing device may further include a supplying
mechanism configured to supply fresh developer including one of
fresh carrier and a mixture of fresh toner and the fresh carrier to
the developer container when the deterioration of the developer is
detected, and a collecting mechanism configured to collect excess
developer.
A user may be allowed to control a supplying operation performed by
the supplying mechanism.
Further, in one embodiment, a novel method of detecting
deterioration of developer includes filling a developer including a
toner and a carrier in a developing device, delivering the
developer toward an image bearing member disposed in a vicinity of
the developing device, and detecting deterioration of the developer
based on a predetermined characteristic of the developer.
Further, in one embodiment, a novel image forming apparatus
includes an image bearing member and a developing device. The image
bearing member is configured to bear an electrostatic latent image
formed on a surface thereof. The developing device is configured to
develop the electrostatic latent image into a toner image with
toner, and includes a developer container configured to contain a
developer including a toner and a carrier, a developer delivering
mechanism configured to deliver the developer toward the image
bearing member, and a detecting mechanism configured to detect
deterioration of the developer based on a predetermined
characteristic of the developer.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the
attendant advantages thereof will be readily obtained as the same
becomes better understood by reference to the following detailed
description when considered in connection with the accompanying
drawings, wherein:
FIG. 1 is a schematic structure of an image forming apparatus
according to an exemplary embodiment of the present invention;
FIG. 2 is a schematic structure of a developing device included in
the image forming apparatus of FIG. 1;
FIG. 3 is a perspective view of the developing device of FIG.
2;
FIG. 4 is a horizontal cross sectional view of a developer
container of the developer device, viewed from a top of the
developer container;
FIG. 5 shows a structure of a second conveying screw included in
the developing device of FIG. 2;
FIG. 6 is a graph showing a relationship of an output voltage and a
toner density of developer contained in the developing device;
FIG. 7 is a graph showing an example of a detecting method of
deterioration of developer;
FIG. 8 is a graph showing another example of the detecting method
of deterioration of developer;
FIG. 9 is a graph showing another example of the detecting method
of deterioration of developer;
FIG. 10 is a graph showing a correlation between a developer charge
and an amount of developer carried by a developer carrying
member;
FIG. 11A is a plane view of the developer carried by the developer,
carrying member having an amount of developer;
FIG. 11B is a plane view of the developer carried by the developer
carrying member having another amount of developer;
FIG. 12 is a graph showing a correlation between an output voltage
of a developer volume sensor and an amount of developer carried by
the developer carrying member;
FIG. 13A is a front view of the developer carried by the developer
carrying member having an amount of developer;
FIG. 13B is a front view of the developer carried by the developer
carrying member having another amount of developer;
FIG. 14 is a graph showing a correlation of a resistance value
between the developer carrying member and a developer regulating
member and an amount of developer carried by the developer carrying
member;
FIG. 15A is a graph showing a correlation between a drive time of
the developing roller and a surface roughness of the developer
carrying member;
FIG. 15B is a graph showing a correlation between the surface
roughness of the developer carrying member and an amount of
developer carried by the developer carrying member;
FIG. 16 is a schematic structure of a toner scattering sensor
included in the developing device of FIG. 2;
FIG. 17 shows a correlation between a toner scattering density and
an output of the toner scattering sensor of FIG. 16; and
FIG. 18 is a graph showing respective degrees of deterioration of
developer including toner and carrier, based on a relative
relationship of degrees of failures such as toner scattering and
contamination and a period of time.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In describing embodiments of the present invention illustrated in
the drawings, specific terminology is employed for clarity.
However, the disclosure of this patent specification is not
intended to be limited to the specific terminology so selected and
it is to be understood that each specific element includes all
technical equivalents that operate in a similar manner.
Referring now to the drawings, wherein like reference numerals
designate identical or corresponding parts throughout the several
views, preferred embodiments of the present invention are
described.
Referring to FIG. 1, a schematic structure of an image forming
apparatus 100 in one exemplary embodiment of the present invention
is described.
The image forming apparatus 100 may be a multi-functional machine
including a plurality of functions of a copier, printer, and
facsimile machine, but the present invention is not limited only to
such an image forming apparatus. For example, an image forming
apparatus of the present invention can be a facsimile machine, a
printer, a copier, or a multi-functional machine having multiple
functions such as of a copier and a printer.
Further, the image forming apparatus 100 has been assumed to
perform image forming operations based on image signals
corresponding to image data received from an external device. In
performing the image forming operations, the image forming
apparatus 100 may print an image on a recording medium, for
example, a plain paper, a sheet in use for an overhead projector
(or an OHP sheet), a heavy paper such as a post card, an envelope,
etc.
The image forming apparatus 100 of FIG. 1 produces a black and
white image, but the present invention is not limited only to such
an image forming apparatus. For example, an image forming apparatus
may produce an image having a plurality of colors such as a
two-color image and a full-color image.
The image forming apparatus 100 includes an image forming mechanism
4, a sheet discharging tray 15, an image reading mechanism 16, a
sheet feeding mechanism 17, a control unit (not shown), a display
unit (not shown), and an operation panel (not shown).
The image forming mechanism 4 includes a plurality of image forming
units for performing the image forming operations.
The sheet discharging tray 15 is arranged substantially in a middle
of a main body of the image forming apparatus 100 between the image
reading unit 16 and the image forming mechanism 4 to have a space
for stacking the recording medium.
The image reading mechanism 16 such as a scanner is disposed at a
position above the sheet discharging tray 15.
The sheet feeding mechanism 17 is disposed at a position below the
image forming mechanism 4.
The control unit (not shown) includes a central processing unit (or
a CPU), a memory, etc., for controlling entire operations of the
image forming apparatus 100.
The display unit (not shown) displays specified information to a
user.
The operation panel includes an input unit (not shown) for allowing
the user to input specified information.
The image forming mechanism 4 includes a photoconductive element 5,
an optical writing device 14, a charging device 6, a developing
device 8, an image density sensor 18, a transfer unit 20, a
cleaning device 2, a discharging device (not shown), a pair of
registration rollers 19, and a fixing device 10.
The photoconductive element 5 is a drum-shape image bearing member
disposed at the center of the image forming mechanism 4 so that an
electrostatic latent image can be formed on a surface thereof.
The optical writing device 14 is disposed at a position above the
photoconductive element 5. The optical writing device 14 reads
image data scanned by the image reading mechanism 16 or image data
output from an external computer (not shown), and controls light
beams L to form an electrostatic latent images on the surface of
the photoconductive element 5.
The charging device 6, the developing device 8, and the image
density sensor 18 are disposed around the photoconductive element 5
in order along rotation direction A in FIG. 1.
The charging device 6 serving as a charging mechanism uniformly
charges the surface of the photoconductive element 5 before the
optical writing device 14 irradiates the surface of the
photoconductive element 5 to form the electrostatic latent
image.
The developing device 8 develops the electrostatic latent image
formed on the photoconductive element 5 into a toner image. Details
of the developing device 8 will be described later.
The image density sensor 18 is a reflection density sensor and is
disposed downstream of the developing device 8. The image density
sensor 18 serves as a toner density sensor to obtain a density of
toner on an image formed on the photoconductive element 5.
The image density sensor 18 includes a light emitting element and a
light receiving element (both not shown in FIG. 1). The light
emitting element emits a light beam toward the toner image, and the
light receiving element receives the light beam reflected by the
toner image to detect a reflection density. The reflection density
indicates a degree of ill-charged toner adhered to a non-image
forming area or non-image forming areas on the surface of the
photoconductive element 5, i.e., a degree of a background
contamination. The image density sensor 18 may also detect an
amount of toner on a reference toner image formed on the
photoconductive element 5, i.e., an image density.
The transfer unit 20 is disposed downstream of the toner density
sensor 18 along the rotation direction A of FIG. 1. The transfer
unit 20 transfers the toner image formed on the surface of the
photoconductive element 5 onto a sheet-type recording medium (not
shown), and conveys the recording medium having the toner image
thereon.
More specifically, the transfer unit 20 is a belt-type transfer
mechanism and includes a belt 21, a driving roller 22, a driven
roller 23, and a contact and separation mechanism (not shown).
The belt 21 includes a rubber material having moderate resistance.
The belt 21 is passed over or surrounds the driving roller 22 that
drives to rotate the belt 21, and the driven roller 23.
The contact and separation mechanism allows the belt 21 to contact
to and separate from the surface of the photoconductive element 5
along with the image forming operations performed by the image
forming apparatus 100.
The cleaning device 2 serving as an cleaning mechanism removes
residual toner on the surface of the photoconductive element 5
after the toner image is transferred onto the recording medium.
The discharging device (not shown) serving as an electronic
discharging mechanism discharges the photoconductive element 5 to
remove residual electric charge from the surface of the
photoconductive element 5 after the residual toner is removed from
the surface of the photoconductive element 5.
The pair of registration rollers 19 controls intervals for a black
and white image to be properly transferred onto the recoding
medium. The recording medium fed from the sheet feeding mechanism
17 is conveyed to a portion between the photoconductive element 5
and the transfer unit 20 in synchronization with the pair of
registration rollers 19.
The fixing device 10 serving as a fixing mechanism fixes the toner
image transferred from the photoconductive element 5 by the
transfer unit 20. The fixing device 10 includes a heat roller 25
and a pressure roller 26. The heat roller 25 applies heat to the
toner image formed on the recording sheet to melt the toner on the
toner image, and the pressure roller 26 applies pressure to the
toner image to fix the toner image to the recording sheet.
The sheet feeding mechanism 17 includes sheet feeding trays 31, a
duplex tray 32, sheet feeding rollers 33, and sheet conveying
rollers 34.
The sheet feeding trays 31 are respectively disposed at a plurality
of vertically different steps and can accommodate different sizes
of sheets.
The duplex tray 32 is disposed at a position above the uppermost
sheet feeding tray 31. The duplex tray 32 receives the recording
sheet, on one side of which a toner image is formed. The recording
sheet is fed to the duplex unit 32 after the recording sheet is
switched back. The duplex sheet 32 then transports the recording
sheet to the image forming mechanism 4 to have another image formed
on the other side of the recording sheet.
The sheet feeding rollers 33 feed the recording sheet accommodated
in the sheet feeding trays 31 and the duplex tray 32 toward the
image forming mechanism 4.
The sheet conveying rollers 34 receive the recording sheet from the
respective sheet feeding rollers 33, and further convey the
recording sheet toward the image forming mechanism 4.
The above-described image forming apparatus 100 obtains image data
e.g. by receiving such image data from the external computer. When
the image forming apparatus 100 receives the image data, the
photoconductive element 5 rotates in the rotation direction A as
shown in FIG. 1 and is uniformly charged with the charging device
6. The optical writing device 14 emits the light beam L passing
between the charging device 6 and the developing device 8 toward
the photoconductive element 5, as shown in FIG. 1, and irradiates
the photoconductive element 5 with the light beam L corresponding
to the image data, so that an electrostatic latent image
corresponding to the image data may be formed on the surface of the
photoconductive element 5. The electrostatic latent image formed on
the photoconductive element 5 is developed to a toner image with
the developer including toner at the developing device 8. That is,
the photoconductive element 5 is charged by the charging device 6,
is irradiated by the light beam L emitted by the optical writing
unit 14 to form an electrostatic latent image, and is developed by
the developing device 8.
The toner image formed on the photoconductive element 5 is then
transferred onto the recording sheet fed by the sheet feeding
mechanism 17.
The recording sheet is fed from one of the sheet feeding trays 31
of the sheet feeding mechanism 17. When the sheet feeding roller 33
corresponding to the one of the sheet feeding trays 31 is rotated
by a drive motor (not shown), the recording sheet placed on the top
of a stack of transfer sheets in the one of the sheet feeding trays
31 is fed and conveyed toward a portion between rollers of the pair
of registration rollers 19. The recording sheet is fed to the image
forming mechanism 4 in synchronization with the pair of
registration rollers 19 so that the toner image formed on the
surface of the photoconductive element 5 is transferred onto a
proper position of the recording sheet. Accordingly, the recording
sheet is fed and the toner image is transferred from the
photoconductive element 5 onto the recording sheet.
The toner image on the recording sheet is fixed by the fixing
device 10 through the application of heat and pressure. The
recording sheet having the fixed image is then discharged to the
sheet discharging tray 15.
After the toner image is transferred to the recording sheet, the
residual toner on the surface of the photoconductive element 5 is
removed by the cleaning device 2 and the residual electricity on
the surface of the photoconductive element 5 is discharged by the
discharging device.
Referring now to FIGS. 2 to 5, details of the developing device 8
are described.
As shown in FIG. 2, the developing device 8 includes a developer
container 55, a developing roller 51, a developing blade 52, first
and second conveying screws 53 and 54, and a toner density sensor
90 including a detecting portion 90a.
The developer container 55 is a casing having an opening facing the
photoconductive element 5 and accommodates the developer therein.
The developer container 55 further includes a developing chamber
58, an agitating chamber 59, and a partition 81, which is a partial
partition, which will be described later. The developer container
55 further includes an inlet 91 and an outlet 64 for replacing the
developer, which will be described later.
The developing roller 51 serving as a developer carrying member is
disposed at a position closely facing the photoconductive element 5
and rotates in a direction indicated by arrow E in FIG. 2.
The developing roller 51 includes a developing sleeve (not shown)
and a magnet roller (not shown).
The developing sleeve includes a non-magnetic material having a
cylindrical shape and is driven to rotate in the direction E. The
developing sleeve included in the developing roller 51 includes an
aluminum material, but the present invention is not limited to such
a developing sleeve. For example, the embodiment of the present
invention may have a non-magnetic material such as brass,
stainless, electrically conductive materials, etc.
The magnet roller includes a plurality of magnets and is fixedly
disposed at an inside of the developing sleeve.
The developing blade 52 serving as a developer regulating member
regulates a height of a layer of the developer conveyed onto the
surface of the developing roller 51.
The developing blade 52 may be an aluminum extrusion, stainless
steel, etc., and be fixedly disposed facing a surface of the
developing sleeve with a gap of several hundred microns from the
surface of the developing sleeve.
Due to magnetic force generated by the magnet roller in the
developing roller 51, the developer is magnetically attracted to
the surface of the developing sleeve to form a magnetic brush. The
developer is then conveyed on the surface of the developing sleeve
along with the rotation of the developing sleeve. After the
developing blade 52 uniformly regulates the height of the
developer, the developer is conveyed to the surface of the
photoconductive element 5.
As previously described, the developer contains toner and carrier.
Even though the developer is conveyed to the surface of the
photoconductive element 5, the toner in the developer
electrostatically adheres to the electrostatic latent image formed
on the photoconductive element 5 so that the electrostatic latent
image is visualized as a toner image. Unused toner and the carrier
conveyed with the toner are conveyed back to the developing device
8 along with the rotation of the developing sleeve.
The first and second conveying screws 53 and 54 are disposed in
parallel to each other to circulate and agitate the developer, as
shown in FIG. 4, and are disposed in parallel with respect to the
developing roller 51.
The first conveying screw 53 is a conveying auger serving as a
first conveying member. The first conveying screw 53 includes a
shaft 83 and a screw 85. The shaft 83 serves as a core of the
rotation of the first conveying screw 53, rotating in a direction
indicated by arrow B of FIG. 2. The screw 85 is formed on the shaft
83 as a spirally protruded fin.
The second conveying screw 54 is a delivering member as well as a
conveying auger serving as a second conveying member. The second
conveying screw 54 includes a shaft 84 and a screw 86. The shaft 84
serves as a core of the rotation of the second conveying screw 54,
rotating in a direction indicated by arrow C of FIG. 2, which is an
opposite direction as the rotation of the first conveying screw 53.
The screw 86 is formed on the shaft 84 as a spirally protruded
fin.
Further, as shown in FIGS. 4 and 5, a removing member 67 removing
the developer on the detecting portion 90a of the toner density
sensor 90 is adhered or glued to a mounting unit 68 to be
integrally mounted on the second conveying screw 54.
With the rotations of the shafts 83 and 84, the screw 85 of the
first conveying screw 53 and the screw 86 of the second conveying
screw 54 convey the developer toward the developing roller 51,
which is a direction perpendicular to respective lengths of the
shafts 83 and 84.
The first and second conveying screws 53 and 54 rotate in
directions opposite to each other to as to convey the developer in
directions opposite to each other. More specifically, the first
conveying screw 53 rotates in the direction B in FIG. 2 to convey
the developer in a direction from an outward end that is a front
side to an inward end that is the opposite side in FIG. 2, and
conveys the developer from left to right in FIG. 4. The second
conveying screw 54 rotates in the direction C in FIG. 2 to convey
the developer in a direction from an inward end that is an opposite
side to an outward end that is a front side in FIG. 2, and conveys
the developer from right to left in FIG. 4. Further, since the
partition 81 gives space at both ends with respect to inner walls
of the developer container 55, the developer can travel between the
two chambers in a predetermined direction. Accordingly, in the
process in which the developer is conveyed in a constant direction
indicated by arrow D in FIG. 4, the developer can be fully
agitated.
As previously described, the developer container 55 includes the
developing chamber 58, the agitating chamber 59, and the partition
81 as shown in FIG. 2.
The developing chamber 58 includes the first conveying screw 53 and
accommodates developer.
The agitating chamber 59 includes the second conveying screw 54 and
accommodates developer.
The partition 81 serving as a separation plate separates the
developer container 55 into the developing chamber 58 and the
agitating chamber 59. Even through the partition 81 separates the
developer container 55 into two spaces, both ends of the partition
81 in its longitudinal direction do not contact with the developer
container 55 having respective inner walls standing perpendicular
to the ends of the partition 81, as shown in FIG. 4. That is, the
partition 81 can give spaces for the developer to travel between
the developing chamber 58 and the agitating chamber 59 in a
predetermined direction.
The first conveying screw 53 is disposed facing the developing
roller 51 to convey developer to the developing roller 51.
Therefore, the developing chamber 58 is disposed in a closer
position to the developing roller 51 than the agitating chamber
59.
The toner density sensor 90 serves as a toner density detecting
mechanism and detects a density of toner contained in the developer
of the developer container. The toner density sensor 90 is disposed
at the bottom of the agitating chamber 59 so that the detecting
portion 90a of the toner density sensor 90 can monitor the inside
of the agitating chamber 59.
The developing device 8 further includes a developer amount sensor
88 and a toner scattering sensor 89.
The developer amount sensor 88 serves as a detecting mechanism to
obtain an amount of developer carried by the developing roller
51.
The toner scattering sensor 89 serves as a detecting mechanism to
obtain a degree of deterioration of developer in accordance with an
amount of toner scattered out of the developer container 55 of the
developing device 8.
The developing device 8 of FIG. 2 further includes a connecting
unit 40, a collected developer container 47 (see FIG. 3), a
developer transportation path 48, a developer conveying screw 63, a
developer transportation motor (not shown), and a developer
discharging device 49.
The connecting unit 40 connects the developing device with a
supplying mechanism that will be described later.
The collected developer container 47 collects and contains excess
developer discharged from the developer container 55.
The developer transportation path 48 guides the developer
discharged from the developer container 55 to the collected
developer container 47.
The developer conveying screw 63 is rotated by the developer
transportation motor to convey the developer to the collected
developer container 47. The developer conveying screw 63 and the
developer transportation motor may be omitted unless necessary.
The developer discharging device 49 is disposed to connect the
developer container 55 and the developer transportation path
48.
As previously described, the developer container 55 includes the
inlet 91 and the outlet 64.
The inlet 91 is arranged to connect with the connecting unit 40 and
serves as an opening to receive, through the connecting unit 40,
toner and carrier conveyed from the supplying mechanism.
The outlet 64 is arranged to connect with the developer discharging
device 49 and serves as an opening to discharge excess developer
due to an increase of an entire amount of the developer after the
carrier or developer is supplied from the supplying mechanism. The
excess developer can be discharged out of the developer container
55 through the developer discharging device 49 and the developer
transportation path 48 to the collected developer container 47.
In FIG. 3, the developing device 8 further includes a toner
cartridge 41, a toner transportation path 42 (also see FIG. 2), a
toner conveying screw 61 (see FIG. 2), and a toner transportation
motor 43.
The toner cartridge 41 accommodates supplemental fresh toner
therein to supply the fresh toner to the developer container 55.
The fresh toner has the same structure and function as the toner
previously contained in the developer container 55.
The toner transportation path 42 is connected with the connecting
unit 40 and guides the fresh toner accommodated in the toner
cartridge 41 to the developer container 55.
The toner conveying screw 61 is disposed in the toner
transportation path 42 and is rotated by the toner transportation
motor 43 to convey the fresh toner toward the developer container
55.
The developing device 8 further includes a carrier cartridge 44, a
carrier transportation path 45, a carrier conveying screw (not
shown), and a carrier transportation motor 46.
The carrier cartridge 44 accommodates supplemental fresh carrier to
supply the fresh carrier to the developer container 55. The fresh
carrier has the same structure and function as the carrier
previously contained in the developer container 55.
The carrier transportation path 45 is connected with the connecting
unit 40 and guides the fresh carrier accommodated in the carrier
cartridge 44 to the developer container 55. The carrier
transportation path 45 is shown as the same as the toner
transportation path 42 in FIG. 2.
The carrier conveying screw is disposed in the carrier
transportation path 45 and is rotated by the carrier transportation
motor 46 to convey the fresh carrier toward the developer container
55. The carrier conveying screw is shown as the same as the toner
conveying screw 61 in FIG. 2.
The carrier cartridge 44 generally accommodates the supplemental
fresh carrier solely. However, if necessary, the carrier cartridge
44 may accommodate a small amount of the fresh toner mixed with the
fresh carrier. In this case, the carrier cartridge 44 contains
supplemental fresh developer.
The fresh toner contained in the toner cartridge 41 is supplied via
the toner transportation path 42 to the developer container 55 by a
small amount at a time. The fresh carrier or fresh developer
contained in the carrier cartridge 44 is supplied via the carrier
transportation path 45 to the developer container 55 by a small
amount at a time.
According to the above-described operations, the carrier cartridge
44, the carrier transportation path 45, the carrier conveying
screw, the carrier transportation motor 46, and the connecting unit
40 may form the supplying mechanism supplying the fresh carrier or
the fresh developer.
The toner transportation motor 43 controls the number of rotations
of the toner conveying screw 61 to adjust a supplying amount of the
fresh toner. The carrier transportation motor 46 controls the
number of rotations of the carrier conveying screw to adjust a
supplying amount of the fresh carrier or the fresh developer. The
rotations of the toner transportation motor 43 and the carrier
transportation motor 46 are controlled by the control unit.
When the fresh carrier or the fresh developer is supplied from the
carrier cartridge 44 to the developer container 55, the developer
previously accommodated in the developer container 55 may overflow.
The overflowed developer may be discharged via the developer
discharging device 49 and the developer transportation path 48 into
the collected developer container 47.
According to the above-described operations, the collected
developer 47, the developer transportation path 48, the developer
conveying screw 63, the developer transportation motor, and the
developer discharging device 49 may form a collecting
mechanism.
The toner cartridge 41, the carrier cartridge 44, and the collected
developer container 47 are respectively detachable with respect to
the developing device 8. More specifically, the toner cartridge 41
is detachable with respect to the toner transportation path 42 to
be easily replaceable when the fresh toner contained therein runs
out. The carrier cartridge 44 is detachable with respect to the
carrier transportation path 45 to be easily replaceable when the
fresh carrier contained therein runs out. The collected developer
container 47 is detachable with respect to the developer
transportation path 48 to be easily replaceable when the fresh
developer contained therein becomes full.
The transportation systems shown in the embodiment use screws, but
the present invention is not limited only to such transportation
systems. For example, an embodiment of the present invention can be
a developing device with a transportation system using a pump
mechanism such as a pump conveying powder.
In FIG. 4, gears 65 and 66 are disposed outside the developing
device 8 to rotate the first and second conveying screws 53 and 54,
respectively. The gears 65 and 66 are driven by respective driving
motors (not shown) that are controlled by the control unit to
rotate in directions opposite to each other so that the shaft 83 of
the first conveying screw 53 and the shaft 84 of the second
conveying screw 54 may rotate in directions opposite to each
other.
As described above, the developing device 8 having such a structure
agitates the developer by the first and second conveying screw 53
and 54 so that the toner contained in the developer is charged. The
developer contained in the developing chamber 58 is then delivered
to the developing roller 51 and is regulated by the developing
blade 52. The developer regulated to a layer having an appropriate
amount thereof is conveyed to a developing area between the
developing roller 51 and the photoconductive, element 5 along with
the rotation of the developing roller 51 in the direction of the
arrow E. The fully charged toner contained in the developer is
electrostatically delivered to the electrostatic latent image
formed on the surface of the photoconductive element 5 so that the
electrostatic latent image may be visualized to a toner image.
Thus, the developing device 8 performs a developing operation using
two-component developer including non-magnetic black toner and
magnetic carrier. As the developing operation is repeatedly
performed, the amount of toner contained in the developer gradually
reduces. To compensate for the loss of toner in the developer, the
fresh toner is supplied accordingly from the toner cartridge 41 to
maintain a constant toner density of the developer circulating in
the developer container 55. To accordingly supply the fresh toner
into the developer container 55, the control unit performs a
feedback control using the toner density sensor 90.
The developing device 8 is designed such that the fresh toner
supplied through the inlet 91 to the developer container 55 falls
onto the second conveying screw 54 in the process of the feedback
control. That is, the inlet 91 is arranged at a position to supply
the fresh toner to the second conveying screw 54. With the
above-described structure, an image can be uniformly developed.
When the fresh toner directly falls onto the first conveying screw
53, the fresh toner may not be sufficiently agitated to be mixed
with the developer before the fresh toner mixed with the developer
is conveyed to the developing roller 51. Accordingly, the inlet 91
arranged at the position to supply the fresh toner to the second
conveying screw 54 allows the toner to be sufficiently agitated and
uniformly distributed in the developer contained in the first
conveying screw 53 before the fresh toner mixed with the developer
previously contained in the developer container 55 reaches the
developing roller 51. Therefore, the fresh toner supplied to the
developer container 55 as described above may not cause a problem
such as nonuniformity in the developing operation.
Referring to FIG. 6, a characteristic of the developer is
shown.
A substantially linear shape shown in FIG. 6 represents a
characteristic of the developer between a toner density and an
output voltage of the toner density sensor 90. That is, when the
toner density increases, the magnetic permeability decreases, and
the output voltage of the toner density sensor 90 becomes low.
Conversely, when the toner density decreases, the magnetic
permeability increases, and the output voltage of the toner density
sensor 90 becomes high. That is, the toner density can be obtained
in accordance with the output voltage of the toner density sensor
90. The output voltages as shown in FIG. 6 are average values of a
predetermined period of time.
According to the above-described characteristic, when an output
voltage of the toner density sensor 90 increases, it is detected
that the toner density decreases, that is, the toner is consumed.
In that case, the control unit controls the developing device 8 to
supply the fresh toner from the toner cartridge 41 to the developer
container 55.
The toner density sensor 90 is arranged to surely detect magnetic
permeability of the developer. As shown in FIG. 2, the toner
density sensor 90 is disposed at the bottom of the agitating
chamber 59 so that the detecting portion 90a of the toner density
sensor 90 can monitor the inside of the agitating chamber 59.
Since the magnetic permeability of developer may vary in accordance
with a change in environment or in bulk density of developer, a
target output voltage of the toner density sensor 90 is accordingly
calibrated. More specifically, a target output voltage of the toner
density sensor 90 may be measured by the image density sensor 18
and be calibrated in accordance with an output result of image
density of a reference toner image formed on the photoconductive
element 5.
The fresh toner supplied to the developer container 55 is agitated
and mixed by the first and second conveying screws 53 and 54 with
the developer previously contained in the developer container
55.
Since the fresh toner is accordingly supplied as described above,
the toner density in the developer container 55 can be properly
maintained. However, when toner and carrier are repeatedly abraded
and collided, a portion of a toner particle adheres to a carrier
particle, and a surface of the carrier particle may be contaminated
or a coated layer of the carrier particle may be peeled. The
carrier including the contaminated or peeled carrier particles may
cause deterioration of the carrier, gradually reducing a charging
ability of the carrier with respect to the toner, and sharply
reducing image quality.
Therefore, the deteriorated carrier may be replaced to maintain the
charging ability to the toner when the carrier is determined to be
deteriorated. An appropriate amount of carrier is preferably
replaced because unsatisfactory amount of carrier may induce a
lower charging ability of toner and excess amount of carrier may
induce a waste of carrier, which may go against the trend of
effective use of resources, etc.
Instead of additionally providing a device for detecting
deterioration of developer, the developing device 8 employs a
detection method using the toner density sensor 90 to detect
deterioration of developer so that the deterioration of developer
can be detected based on an output waveform of the toner density
sensor 90.
When the carrier deteriorates, a degree of adhesion between the
carrier and toner or between the carriers may increase and the
fluidity of the developer may become worse. With the characteristic
of the carrier, the deterioration of carrier is detected.
To employ the above-described detection method, the developing
device 8 utilizes the removing member 67. As previously described,
the removing member 67 is integrally mounted on the second
conveying screw 54 of the agitating chamber 59 in which the
developer to be detected by the toner density sensor 90 is
accommodated, and removes the developer adhered on the detecting
portion 90a of the toner density sensor 90 as shown in FIGS. 2, 4,
and 5.
As shown in FIG. 4, the removing member 67 includes a film-shape
resin sheet adhered or glued to the mounting unit 68 integrally
mounted to the shaft 84 and the screw 86 of the second conveying
screw 54. The removing member 67 may be flexible to contact with
the detecting portion 90a to remove the developer adhered on the
detecting portion 90a in every cycle of rotation of the second
conveying screw 54. The removing member 67 may be attached to the
mounting unit 68 with an adhesive tape instead of being adhered or
glued thereto.
There are a few millimeters of a clearance between the screw 86 and
an inner wall of the agitating chamber 59 to prevent the screw 86
and the agitating chamber 59 from being damaged due to abrasion
with the developer during rotations by the screw 86. Therefore, the
developer remaining on the detecting portion 90a may not be fully
removed.
By providing the removing member 67, the developer adhered on the
detecting portion 90a may effectively be removed and the developer
in the agitating chamber 59 may effectively be agitated.
As described above, the toner density sensor 90 can detect the
density of toner contained in the developer. In particular, since
the detecting portion 90a of the toner density sensor 90 is
disposed at the bottom of the agitating chamber 59 that is a space
in which the removing member 67 interferes with the developer, the
toner density sensor 90 can surely and effectively detect the toner
density.
Referring to FIGS. 7 to 9, a plurality of detection methods using
the toner density sensor 90 and the related apparatus, device, and
unit are described.
FIG. 7 shows output waveforms of toner densities output by the
toner density sensor 90. When the removing member 67 comes over the
toner density sensor 90 contacting the detecting portion 90a, an
amount of developer adhering on the detecting portion 90a sharply
reduces, so that an output voltage of the toner density obtained by
the toner density sensor 90 may reach its peak value. After the
removing member 67 passes the detecting portion 90a of the toner
density sensor 90, the developer flows over the detecting portion
90a, and the amount of developer gradually increases. When the
removing member 67 rotates by 180 degrees from the detecting
portion 90a along the inner wall of the agitating chamber 59, the
output voltage may reach its bottom value. That is, an output
voltage of the toner density obtained by the toner density sensor
90 may reach its bottom value when a phase of the removing member
67 after rotating 180 degrees is moved from a phase in which the
output voltage reaches the peak value.
As described above, when the carrier deteriorates, a degree of
adhesion between the toner and carrier or between the carriers
increases and fluidity of the developer becomes worse. Therefore, a
period of time between the peak value and bottom value of the
output voltage may be longer as deterioration of carrier increases.
For example, the output waveform in a solid line shown in FIG. 7
represents an output waveform of fresh developer including fresh
carrier, and the output waveform in the dotted line represents an
output waveform when the deterioration of developer proceeds. That
is, a period of time between the peak and bottom values of the
output waveform in the dotted line may be longer than that in the
solid line.
The detection method of detecting deterioration of developer
according to the present invention uses the toner density sensor 90
for detecting toner density so that deterioration of developer or
carrier may be detected based on the output waveforms. Therefore,
deterioration of carrier can surely be detected without inducing an
increase in cost, and an appropriate amount of supplemental carrier
can prevent a shortage of charge ability with respect to toner as
well as a waste of carrier.
More specifically, the detection method of detecting deterioration
of developer according to the present invention uses the toner
density sensor 90 to detect a deterioration of developer based on
output waveforms as follows.
That is, deterioration of developer may be detected based on an
output waveform having a slope of a line between the peak and
bottom values obtained by the toner density sensor 90.
As shown in FIG. 7, as the developer deteriorates, a slope from the
peak value to the bottom value may change from .alpha.1 to
.alpha.2.
For example, an initial slope is measured based on an output
waveform with fresh developer and is stored in a memory of the
control unit as a reference slope. When a slope having a smaller
angle by a predetermined angle than the reference slope is
detected, it is determined that the developer is deteriorated. The
above-described detection is performed based on the output waveform
having the slope measured from the peak value to the bottom value
of the toner density, but an output waveform having a slope
measured from the bottom value to the peak value of the toner
density may also be used.
It is desirable to measure the slope under a condition with a
constant toner density, for example when the initial slope is
measured. A decrease in fluidity of developer may occur due to a
decrease in fluidity of carrier as well as a decrease in fluidity
of toner, thereby a change in toner density may cause the fluidity
of developer to change. When the slope of the output waveform is
measured under the condition with a constant toner density, the
deterioration of toner can be restricted to the minimum. To further
restrict the decrease in fluidity of toner and correctly measure
deterioration of carrier, it is desirable that the slope of the
output waveform is measured under the condition with toner density
lower than the constant toner density.
The deterioration of developer can also be detected based on the
output waveform having a period of time between the peak value and
the bottom value obtained by the toner density sensor 90 along with
or instead of the above-described detection of deterioration of
developer based on the slope.
As shown in FIG. 8, as the developer deteriorates, a period of time
from the peak value to the bottom value may change from T1 to
T2.
For example, an initial period of time is measured based on an
output waveform with fresh developer and is stored in a memory of
the control unit as a reference period of time. When a period of
time longer by a predetermined period of time than the reference
period of time is detected, it is determined that the developer is
deteriorated. The above-described detection is performed based on
the output waveform having the period of time from the peak value
to the bottom value of the toner density that may also be used.
It is desirable to measure the period of time under a condition
with a constant toner density, for example when the initial period
of time is measured. A decrease in fluidity of developer may occur
due to a decrease in fluidity of carrier as well as a decrease in
fluidity of toner, thereby a change in toner density may cause the
fluidity of developer to change, which is based on the same reason
described in the detection based on the output waveform having the
slope. Further, it is also desirable that the period of time of the
output waveform is measured under the condition with toner density
lower than the constant toner density, which is also based on the
same reason described in the detection based on the output waveform
having the slope.
The deterioration of developer can also be detected based on the
output waveform having an output voltage after a predetermined
period of time from a predetermined output value obtained by the
toner density sensor 90 along with or instead of the
above-described detections of deterioration of developer based on
the output waveform having the slope and/or the period of time.
As shown in FIG. 9, as the developer deteriorates, an output
voltage obtained after a predetermined period of time may change
from V1 to V2. In this case, however, the above-described
predetermined period of time is desirably set to be shorter than a
period of time at the peak value or the bottom value of the output
waveform.
For example, an initial output voltage after the predetermined
period of time from the peak value of fresh developer is measured
based on an output waveform with fresh developer and is stored in a
memory of the control unit as a reference output voltage. When an
output voltage having a smaller voltage by a predetermined voltage
than the reference output voltage is detected, it is determined
that the developer is deteriorated.
The above-described detection is performed based on an output
voltage after the predetermined period of time from the peak
voltage of an output waveform of a toner density, but an output
voltage after the predetermined period of time from the bottom
voltage or between the bottom and peak voltages of an output
waveform of the toner density may also be used.
It is desirable to measure an output voltage under a condition with
a constant toner density, for example when the initial output
voltage is measured. A decrease in fluidity of developer may occur
due to a decrease in fluidity of carrier as well as a decrease in
fluidity of toner, thereby a change in toner density may cause the
fluidity of developer to change, which is based on the same reason
described in the detection based on the output waveform having the
slope. Further, it is also desirable that a period of time of the
output waveform is measured under the condition with toner density
lower than the constant toner density, which is also based on the
same reason described in the detection based on the output waveform
of the slope.
In any case of the above-described measurements of a slope, a
period of time, and an output value based on an output waveform,
each reference value is not limited to a value measured under the
condition with fresh developer. The reference value may be a value
previously stored in the memory of the control unit before
shipping.
As described above, the developing device 8 includes the toner
density sensor 90 and a detecting mechanism to detect deterioration
of developer with the above-described detection method.
When deterioration of developer is detected, the control unit
operates the carrier transportation motor 46 to rotate the carrier
conveying screw so that the fresh carrier or the fresh developer
may be supplied through the carrier transportation path 45, the
connecting unit 40, and the inlet 91 to the developer container
55.
When the above-described supplying operation is performed, an
amount of developer in the developer container 55 increases, and a
bulk of the developer accumulated in the developer container 55 may
become greater and higher than a bottom portion of the outlet 64.
Excess developer accumulated higher than the bottom of the outlet
64 overflows, and goes through the developer discharging device 49.
The excess developer is then conveyed by the developer conveying
screw 63 driven by the developer transportation motor, through the
developer transportation path 48, and is collected by the collected
developer container 47.
As described above, the developing device 8 is controlled such that
a discharging amount of developer is determined based on its level
or height of the accumulated developer. When the fresh carrier or
the fresh developer is supplied to the developer container 55, the
developer contained in the developer container 55 may be discharged
by an amount corresponding to the supplied amount of the fresh
carrier or the fresh developer so that the carrier previously
contained in the developer container 55 can be replaced. The
control unit performs a feedback control to continue the supplying
operation until the deterioration of developer is no longer
detected.
In the process of the feedback control, the fresh carrier or
developer supplied through the inlet 91 to the developer container
55 may be agitated and uniformly distributed in the developer
previously contained in the developer container 55 from a point of
time when the fresh carrier or fresh developer falls onto the
second conveying screw 54 to a point of time when the developer
mixed with the fresh carrier or fresh developer reaches the
developing roller 51 before the developing operation. With the
above-described operation, a problem such as nonuniformity may not
occur in the developing operation.
Further, the developing device 8 allows a user to control the
supplying operation of the fresh carrier or developer.
When deterioration of developer is detected, the control unit
included in the image forming apparatus 100 can give instructions
to the display unit included in the operation panel to indicate
that the deterioration of developer is detected in the image
forming apparatus 100 including the developing device 8, and allow
the user to control the supplying operation of the fresh carrier or
developer through an input unit included in the operation
panel.
The control of the supplying operation may allow the user to change
a threshold to detect the deterioration of developer according to
image quality of an image on the recording sheet. That is, when the
user determines the image on the recording sheet has good image
quality, the user may operate the input unit to adjust the
threshold used to detect the deterioration of developer. When the
user determines the image quality is good, the threshold can be set
to a lower level to reduce the number of supplying operations. When
the user determines the image needs better image quality, the
threshold can be set to a higher level to increase the number of
the supplying operations. The input unit can have additional keys
such as an image quality selection key corresponding to the setting
of the threshold so that levels of image quality can be
selected.
Further, an embodiment of the present invention can arrange the
control performed by the user such that the user can give
instructions to continue the image forming operation without
supplying the fresh developer when the user determines the image
formed on the recording sheet has good image quality.
Setting a lower level of the threshold and/or continuing an image
forming operation may limit an amount of fresh developer and can
prevent excess consumption of developer. Setting a higher level of
the threshold can meet with demands from a user requiring or
preferring a higher quality in an image.
With the above-described operations, the display unit may function
as a display mechanism displaying the results of the
above-described detection and the input unit may function as an
arranging mechanism arranging the above-described supplying
operations.
As previously described, the supplying mechanism supplying the
fresh carrier includes the carrier cartridge 44, the carrier
transportation path 45, the carrier conveying screw, the carrier
transportation motor 46, and the connecting unit 40. The supplying
mechanism may continuously supply the fresh carrier for a
predetermined number of times. However, when deterioration of
developer is still detected or when a detection result such as a
detected value is not in an appropriate range even after the
above-described continuous supplying operation, the supplying
mechanism can stop the supplying operation and issue a warning
through the display unit. The warning may avoid unnecessarily
supplying or discharging the developer when the deterioration of
developer is detected due to an unexpected factor so that the unit
can be stopped, to allow performing an examination of the status
and a maintenance of the unit.
The above-described detection method of the deterioration of
developer may be performed with the toner density sensor 90 serving
as a detection unit so that the deterioration of developer can be
detected based on a characteristic of fluidity of the developer
agitated and conveyed by the second conveying screw 54.
However, the present invention is not limited to the
above-described detection method. An embodiment of the present
invention can detect deterioration of the developer with the
developer amount sensor 88. The developer amount sensor 88 serving
as a detection unit can detect the deterioration of developer based
on a characteristic of amount of developer carried by the
developing roller 51 as a developer carrying member.
The detection method according to the present invention may also be
performed with a torque sensor (not shown in figure), the image
density sensor 18, and the toner scattering sensor 89.
The torque sensor serving as a toner detecting mechanism to obtain
a degree of the deterioration of toner contained in the developer
is a detecting unit to detect deterioration of developer based on a
characteristic of fluidity of the developer agitated and conveyed
by the first and second conveying screws 53 and 54 included in the
developer delivering mechanism.
The image density sensor 18 serving as a background contamination
sensor to obtain a degree of contamination of the developer is a
detection unit to detect deterioration of developer based on a
characteristic of charging ability of the developer carried and
conveyed by the photoconductive element 5.
The toner scattering sensor 89 serving as a detection sensor is a
detection unit to detect deterioration of developer based on a
characteristic of charging ability of the developer carried and
conveyed by the photoconductive element 5 and the developing roller
51.
The following show a plurality of detection methods using the
developer volume detecting sensor 88, the torque sensor, the image
density sensor 18, and/or the toner scattering sensor 89 with the
related apparatus, device, and unit. The descriptions will
generally be given focusing on the characteristics different from
the detection methods using the above-described toner density
sensor 90.
The detection method of deterioration of the developer using the
developer amount sensor 88 is as follows.
As previously described, the developer is magnetically attracted by
magnetic force generated by the magnet roller in the developing
roller 51, and is conveyed over the rough surface of the developing
sleeve using surface roughness thereof. It has been proved that
there is a relationship between an amount of developer charge and
an amount of developer conveyed or attracted to the developing
roller 51 as shown in FIG. 10 when a degree of the surface
roughness of the developing sleeve is constant. More specifically,
when the amount of developer charge is large, the amount of
developer on the developing roller 51 may be large. Conversely,
when the amount of developer charge is small, the amount of
developer on the developing roller 51 may be small.
With the relationship between the amount of developer charge and
the amount of developer on the developing roller 51, an amount of
developer charge can be calculated based on the amount of developer
on the developing roller 51 so that a charging failure due to
deterioration of developer can be detected. In this embodiment, the
above-described relationship is used to obtain the amount of
developer on the developing roller 51 so that the deterioration of
developer can be determined based on the amount of developer charge
obtained by the amount of developer on the developing roller
51.
To obtain the amount of developer on the developing sleeve, an
optical sensor can be used to obtain a parameter, for example, a
reflection density of the developing sleeve, a resistance between
the developing blade 52 and the developing sleeve, the height of a
point of a magnetic brush, etc. In this embodiment, the developer
amount sensor 88 is used to obtain the reflection density, the
resistance, and the height of the magnetic brush. However, the
present invention is not limited to obtaining such parameters using
the developer amount sensor 88.
Referring to FIGS. 11A to 12, obtaining the reflection density of
the developing sleeve is described.
When the amount of developer on the developing sleeve is large as
shown in FIG. 11A, a magnetic brush is thickly formed, and thereby
the developer volume sensor 88 may obtain a small amount of the
reflection density. Conversely, when the amount of developer on the
developing sleeve is small as shown in FIG. 111B, a magnetic brush
is thinly formed, and a large amount of area on the surface of the
developer sleeve is exposed, and thereby the developer volume
sensor 88 may obtain a large amount of the reflection density.
Therefore, a relationship between the output results of the
developer amount sensor 88 serving as a reflection density sensor
and the amount of developer on the developing sleeve may be
indicated as shown in FIG. 12.
Next, obtaining the height of a point of the magnetic brush is
described.
To obtain the height of the magnetic brush, a surface roughness may
be measured without contacting the surface. The developer amount
sensor 88 serving as a surface roughness measuring sensor measures
a height profile of developer in a constant area on the surface of
the developing sleeve to obtain an average value of the heights.
The measured average value of the heights indicates an average
height of the magnetic brush, so the amount of developer on the
developing sleeve may be obtained by multiplying a value of the
entire surface of measured areas.
Referring to FIGS. 13A to 14, obtaining of the resistance between
the developing sleeve and the developing blade 52 is described.
When the amount of developer on the developing sleeve is large, the
developer directly under the developing blade 52 is thickly formed
as shown in FIG. 13A, and thereby the developer volume sensor 88
may obtain a large number of magnetic brush per a unit area.
Conversely, when the amount of developer on the developing sleeve
is small, the developer directly under the developing blade 52 is
thinly formed as shown in FIG. 13B, and thereby the developer
volume sensor 88 may obtain a small number of magnetic brush per a
unit area. According to the above-described results, it is
determined that a specific resistance per a point of the magnetic
brush is substantially identical to the other points thereof.
Therefore, as shown in FIG. 14, when the amount of developer on the
developing sleeve is large and the magnetic brush is thickly
formed, the resistance between the developing sleeve and the
developing blade 52 may be small. Conversely, when the amount of
developer on the developing sleeve is small and the magnetic brush
is thinly formed, the resistance between the developing sleeve and
the developing blade 52 may be large.
Thus, when the amount of developer on the developing sleeve or the
developer carrying member is obtained with a plurality of methods
as described above and the deterioration of developer is detected,
a detection having higher accuracy may be performed. The amount of
developer on the developing sleeve or the developer carrying member
may be obtained using a method other than the above-described
methods. The amount of the developer on the developing sleeve or
the developer carrying member may be obtained using the plurality
of methods in combination that is not specifically limited.
However, it is preferable the combination can achieve higher
accuracy of detection. When a single and efficient accuracy can be
obtained, it is not necessary to perform the plurality of methods
in combination.
When the toner density is constant in detecting the amount of
developer on the developing sleeve or the developer carrying member
is constant, the accuracy in detection may increase. For example,
when the toner density is the same as that of an initial amount of
developer, the accuracy in detection may increase. More
specifically, the accuracy in obtaining the reflection density may
increase because the reflection density reflected by the magnetic
brush becomes uniform. The accuracy in obtaining the height of the
magnetic brush may increase because a volume of a toner particle is
cancelled or ignored. The accuracy in obtaining the resistance
between the developing sleeve and the developing blade 52 may
increase because variations of specific resistance of a single
magnetic brush become small.
The developer amount sensor 88 is disposed upstream of the
developing blade 52 in the direction of the arrow E that is a
direction to which the developer is conveyed by the developing
roller 51. With the above-described structure, a detection may be
performed at an average height of points of the magnetic brush,
thereby preventing variations in detection conditions so that the
accuracy of detection may increase in obtaining the reflection
density, the height of points of the magnetic brush, and the
specific resistance.
The developer amount sensor 88 serving as a reflection density
sensor includes sensors having the same parts as the image density
sensor 18. This allows the amount of developer on the developing
sleeve or the developer carrying member to be detected without
using additional parts, which can bring a reduction in cost.
With the above-described methods, an actual amount of developer on
the developing sleeve or the developer carrying member is detected
to compare with a lower limitation value A of a predetermined
amount of developer on the developing sleeve or the developer
carrying member, for example, see FIGS. 2 and 4. When the actual
amount of developer is lower than or equal to the lower limitation
value A, it is determined that the developer is deteriorated,
thereby supplying the fresh developer. When the actual amount of
developer is greater than the lower limitation value A, it is
determine that the developer is not yet deteriorated and no
supplying operation may be performed.
The developer amount sensor 88 may detect the deterioration of
developer at the following points of time.
To detect the deterioration of developer with higher accuracy, the
amount of developer on the developer sleeve or the developer
carrying member may be detected at a point of time the developer is
fully charged after the developing operation for a predetermined
period of time, a period of time the charging operation is started,
i.e. during a warm-up time, and/or after a predetermined period of
time an amount of developer charge is reduced due to a stop of the
charging operation. For the amount of developer obtained at the
point of time when the charging is started and at the point of time
when an amount of developer charge is reduced, the deterioration of
developer may be determined based on the change in amounts of
developer that rises or falls during a constant period of time.
More specifically, the deterioration of developer may be detected
as follows.
First, the developing roller 51 and other developer delivering
mechanisms such as the first and second conveying screws 53 and 54
stop a developer conveying operation including agitation and
mixing, and the developer amount sensor 88 detects the amount of
developer on the developing sleeve or the developer carrying member
after a predetermined period of time from the stop of the developer
conveying operation. Then, the developing roller 51 and the first
and second conveying screws 53 and 54 resume the developer
conveying operation, and the developer amount sensor 88 detects the
amount of developer on the developing sleeve or the developer
carrying member after a predetermined period of time from the start
of resuming the developer conveying operation. Both amounts of
developer detected by the developer amount sensor 88 may be
compared to detect the deterioration of developer.
With the above-described detection, the change in developer charge
in a period of agitation is cancelled or ignored because the
developer has lower charge due to insufficient agitation, which
cannot be counted as a cause of deterioration of the developer.
Therefore, the high accuracy detection may be achieved.
Further, since the speed of charging and the amount of developer
charge in insufficient agitation are different between fresh
developer and deteriorated developer, the deterioration of
developer may also be detected in high accuracy. That is, the
above-described detection is performed focusing on differences in
the speed of charging and the amount of developer charge according
to a degree of deterioration of developer.
The deterioration of developer is generally detected when the
developer is sufficiently agitated. However, there may be a case in
which the fresh developer that is sufficiently agitated has a same
amount of developer charge as the deteriorated developer that is
also sufficiently agitated. While the developer conveying operation
is not performed, the developer charge of the deteriorated
developer may be lower than that of the fresh developer. Therefore,
the developer charge of the developer not agitated may also be
obtained as follows.
The developer amount sensor 88 detects the amount of developer on
the developing sleeve or the developer carrying member before a
warm-up operation at a power-on to the image forming apparatus 100.
Then, the developer amount sensor 88 detects the amount of
developer on the developing sleeve or the developer carrying member
when the warm up is performed after the above-described detection.
Both amounts of developer detected by the developer amount sensor
88 may be compared to detect the deterioration of developer.
Also with the above-described detection, the change in developer
charge in a period of agitation is cancelled or ignored. Therefore,
the high accuracy detection may be achieved.
Further, as described above, the speed of charging and the amount
of developer charge in insufficient agitation are different between
fresh developer and deteriorated developer, so the deterioration of
developer may also be detected in high accuracy. Further, a period
of time for the detection may be reduced to compensate for the warm
up time.
The deterioration of developer may also be detected based on the
condition of developer after stopping the developer conveying
operation.
First, the developer amount sensor 88 detects the amount of
developer on the developing sleeve or the developer carrying member
while the developing roller 51 and other developer delivering
mechanisms such as the first and second conveying screws 53 and 54
are performing the developer conveying operation including
agitation and mixing. Then, the developer amount sensor 88 detects
the amount of developer on the developing sleeve or the developer
carrying member after a predetermined period of time from the stop
of the developer conveying operation. Both amounts of developer
detected by the developer amount sensor 88 may be compared to
detect the deterioration of developer.
Thus, the deterioration of the developer may be detected in high
accuracy when the developer charge decreases after stopping the
developer conveying operation. That is, the above-described
detection is performed focusing on a difference of the speed of
discharging and the amount of developer charge according to a
degree of deterioration of developer.
The deterioration of developer may also be detected based on a
printing operation of the developing device 8 as follows.
The developer amount sensor 88 detects the amount of the developer
on the developing sleeve or the developer carrying member when the
image forming apparatus 100 performs the printing operation using
the developing device 8. More specifically, the developer amount
sensor 88 detects the amount of the developer on the developing
sleeve or the developer carrying member at a point of time a
predetermined number of images is output from the image forming
apparatus 100. The detection of the amount of developer on the
developing sleeve or the developer carrying member may be performed
in synchronization with the output of image performed by the user,
so a period of time for detection may be reduced.
Further, the detection may be performed with the developer amount
sensor 88 when the developing roller 51 and other developer
delivering mechanisms such as the first and second conveying screws
53 and 54 perform the developer conveying operation including
agitation and mixing. This is because the change in developer
charge in a period of agitation can be cancelled or ignored and the
deterioration of developer can be detected when the developer has
lower charge due to insufficient agitation. That is, the
above-described detection is performed focusing on a difference of
the speed of charging and the amount of developer charge according
to a degree of deterioration of developer.
The detection may also be performed with the developer amount
sensor 88 when the developer conveying operation is performed,
and/or when the fresh toner is supplied, etc.
A combination of these detections may increase accuracy of
detecting the amount of developer on the developer carrying
member.
Now, it is preferable to understand that the amount of developer on
the developer sleeve may be varied according to the condition of a
surface roughness of the developing sleeve. The surface roughness
of the developing sleeve depends on a forming of rough surface of
the developing sleeve and an abrasion due to aging of the
material.
According to the reason described above, it is preferable that a
hardness of the surface of the developing sleeve be greater than
that of the developer. The hard surface thereof may be achieved by
coating the surface of the developing sleeve and/or carefully
selecting the material of the developing sleeve. The developing
sleeve having such a hard surface can avoid wear on the developing
sleeve due to abrasion between the developing sleeve and developer,
carrier in particular. The developing sleeve having such a surface
can also prevent change in roughness thereof. With the
above-described developing sleeve, a change of the amount of
developer on the developing sleeve may be considered as a change of
the amount of developer charge, thereby increasing accuracy of
detection.
In a case in which the surface of the developing sleeve includes a
soft material, a significant change in surface roughness can be
estimated. To surely obtain the degree of the deterioration of
developer based on the amount of developer on the developing
sleeve, the deterioration of developer may be detected in
accordance with a relationship between the period of the developer
conveying operation performed by the developing roller 51 and the
surface roughness of the developing sleeve, as shown in FIG. 15A,
and a relationship between the surface roughness of the developing
sleeve and the amount of developer on the developing sleeve, as
shown in FIG. 15B.
More specifically, a relationship of the surface roughness of the
developing sleeve and the amount of fresh developer of the
developing sleeve is previously obtained. According to the
above-described relationship, an amount of the fresh developer and
an amount of the actual developer are compared under the condition
that the surface roughness of the developing sleeve is identical so
that the deterioration of developer can be detected.
According to the relationship as shown in FIG. 15A, the surface
roughness of the developing sleeve can be obtained. According to
the relationship as shown in FIG. 15B, the amount of fresh
developer can be obtained based on the surface roughness obtained
as described above. By comparison of the amount of the fresh
developer with the amount of the actual developer, the amount of
decrease of the developer charge can be obtained so that the
deterioration of developer can be detected.
Before detecting the deterioration of developer, a developer rate R
of the actual developer on the developing sleeve with respect to
the amount of the fresh developer can be determined. The developer
rate R is substantially a rate of the amount of developer charge of
the actual developer obtained with respect to the amount of
developer charge of the fresh developer. When a developer rate
obtained based on results of the detection is equal to or less than
the developer rate R, the fresh carrier may be supplied to the
developer container 55. Thereby, the deterioration of developer can
be detected under the condition the surface roughness of the
developing sleeve may vary. With the above-described operation, a
change of the amount of developer on the developing sleeve due to a
difference of the amounts of developer charge and a change of the
amount of developer on the developing sleeve due to a difference of
the degree of the surface roughness can be determined, thereby
detecting the deterioration of developer in high accuracy.
Further, the developing device 8 allows the user to control the
supplying operation of the fresh carrier or the fresh developer,
according to the same reasons as described above.
As previously described, the supplying mechanism supplying the
fresh carrier includes the carrier cartridge 44, the carrier
transportation path 45, the carrier conveying screw, the carrier
transportation motor 46, and the connecting unit 40. The supplying
mechanism may continuously supply the fresh carrier for a
predetermined number of times. However, when deterioration of
developer is still detected, the supplying mechanism stops the
supplying operation and issues a warning through the display unit,
also for the same reasons as described above. More specifically,
when the amount of developer on the developer carrying member
remains below a predetermined amount of developer even if the
supplying operation is performed for the predetermined number of
times, or when an unexpected value is obtained, the supplying
operation may be stopped to issue the warning through the
displaying unit.
As described above, the developing device 8 includes the developer
amount sensor 88 and can perform the detection of the deterioration
of developer based on the above-described characteristics of the
developer.
The following show the methods using the torque sensor, the image
density sensor 18, and the toner scattering sensor 89.
The image density sensor 18 is a detecting mechanism to detect an
amount of insufficiently charged toner.
The toner scattering sensor 89 is disposed in a vicinity of the
outside of the developer container 55, below the developer
container 55, and downstream of an area opposite to the
photoconductive element 5 in the rotation direction of the
developing sleeve. As an alternative, the toner scattering sensor
89 can be disposed at a position above the developer container 55
or upstream of an area opposite to the photoconductive element 5 in
the rotation direction of the developing sleeve.
As shown in FIG. 16, the toner scattering sensor 89 includes a
light emitting unit 71 and a light receiving unit 72.
The light emitting unit 71 emits a light beam, and includes a light
emitting element 73, a housing 74 for the light emitting element
73, and a lens 75 that is disposed at a position covering an
opening of the housing 74 in which the light beam emitted by the
light emitting element 73 passes out from the housing 74. The light
receiving unit 72 receives the light beam emitted by the light
emitting unit 71 and reflected from scattered toner. The light
receiving unit 72 includes a light receiving element 76, a housing
77 for the light receiving element 77, and a lens 78 that is
disposed at a position covering an opening of the housing 77 in
which the reflected light beam comes through.
When toner scattering occurs, the scattered toner passes between
the light emitting unit 71 and the light receiving unit 72 included
in the toner scattering sensor 89. At this time, the light beam
emitted from the light emitting element 73 of the light emitting
unit 71 is reflected by scattered toner. The light beam reflected
by the scattered toner is received by the light receiving element
76 of the light receiving unit 72. The reflected light beam is
read, is converted into an electric signal, and is output. The lens
75 is used to improve an efficiency of an outgoing light from the
light emitting element 73, and the lens 78 is used to improve an
efficiency of an incident light to the light receiving element
76.
The result of detection of toner scattering performed by the toner
scattering sensor 89 is shown in FIG. 17.
The torque sensor obtains torque values of the first and second
conveying screws 53 and 54 during the developer conveying
operation, and detects the deterioration of developer based on the
fluidity of developer.
The deterioration of developer is detected as the deterioration of
carrier. More specifically, the image density sensor 18 and the
toner scattering sensor 89 detect a degree of deterioration of
developer and the torque sensor detects a degree of deterioration
of toner, so that a degree of deterioration of carrier can be
estimated and the deterioration of developer may be detected based
on the deterioration of carrier.
In this embodiment, the deterioration of developer, more
specifically the deterioration of toner and carrier, is detected
using the image density sensor 18 together with the toner
scattering sensor 89, but the present invention is not limited to
the detection using these two sensors 18 and 89. An embodiment of
the present invention can detect deterioration of toner and carrier
using only either one of the image density sensor 18 and the toner
scattering sensor 89. The image density sensor 18 detects
background contamination on an area other than the image area, i.e.
on a background area in a which no image is formed on the recording
sheet. The toner scattering sensor 89 detects an amount of
scattered toner. Background contamination and toner scattering may
occur due to insufficiently charged toner or oppositely charged
toner. These toners may adhere to non-image areas on the surface of
the photoconductive element 5 or may depart from carrier in the
magnetic brush formed by centrifugal force generated by rotation of
the developing sleeve, resulting in scattering out of the developer
container 55.
Generally, an amount of insufficiently charged toner and that of
oppositely charged toner in developer tend to increase with age
because of stress applied by the developer when the image forming
operation is repeatedly performed. The amount of developer charge
may be reduced due to a condition of toner or carrier.
Toner is mixed with an additive agent to improve fluidity, secure
the amount of toner charge, and improve anti-electric stability
against environmental variations. However, when the toner is
repeatedly agitated, the additive agent may be separated from a
toner particle or may be buried into a toner particle, which
results in degradation of charging ability. A charging control
agent contained in a toner particle may also deteriorate due to
stress and degrade the charging ability.
When carrier is repeatedly agitated, abrasion and collision with
toner may continuously occur, and a portion of a toner particle may
adhere to a carrier particle, resulting in contamination on the
surface of the carrier particle and peeling of a coat layer of the
carrier particle. This is why the charging ability of carrier with
respect to toner degrades.
As described above, a single toner particle may deteriorate because
agitation of developer allows the additive agent to be separated
from or be buried into the toner particle. The reduction of the
additive agent increases adhesion between the toner particles and
between the toner particle and the carrier particle, resulting in
fluidity reduction of toner. Therefore, a detection of a change in
fluidity of toner can obtain a degree of deterioration of toner. As
the fluidity of toner decreases, a load for agitating developer may
increase. So, if the torque sensor can obtain the load of a
developing unit, the change of fluidity of toner can be obtained,
thereby detecting deterioration of toner.
It is desirable that this detection of deterioration of toner be
performed under the condition with a constant toner density, for
example, when the initial angle of the slope is measured. This is
because the fluidity of developer may depend on the toner density.
Therefore, the measurement of deterioration of toner in the
constant toner density may prevent adverse effects to the toner
density.
As shown in FIG. 18, a degree of deterioration of developer
obtained by detections of amounts of toner scattering and
background contamination may include deteriorations of carrier and
of toner. If the degrees of deteriorations of developer and toner
are obtained, a degree of deterioration of carrier may also be
obtained. More specifically, a correlation of a value of
deterioration of the toner with flesh carrier and a value of
deterioration of the entire developer due to background
contamination and toner scattering is previously obtained. Then,
the value of deterioration of the toner is subtracted from the
value of the deterioration of the entire developer, so that the
degree of deterioration of carrier can be obtained. According to
the degree of deterioration of carrier obtained as described above,
the fresh carrier may be supplied and the carrier having lower
charging ability previously in the developing device 8 may be
discharged from the developing device 8. Thus, the carrier in the
developer device 8 may be replaced, which can produce images having
a constant image quality and minimize the amount of carrier to be
used.
As described above, the developing device 8 includes the torque
sensor, the image density sensor 18, and the toner scattering
sensor 89, and can perform the detection of the deterioration of
developer based on the above-described characteristics of the
developer.
Further, the developing device 8 allows the user to control the
supplying operation of the fresh carrier or the fresh developer,
for the same reasons as described above.
As previously described, the supplying mechanism supplying the
fresh carrier includes the carrier cartridge 44, the carrier
transportation path 45, the carrier conveying screw, the carrier
transportation motor 46, and the connecting unit 40. The supplying
mechanism may continuously supply the fresh carrier for a
predetermined number of times. However, when deterioration of
developer is still detected, the supplying mechanism stops the
supplying operation and issues a warning through the display unit,
also for the same reasons as described above.
The above-described structure of the toner detecting mechanism
employs the torque sensor, but the present invention is not limited
to such a toner detecting mechanism. As an alternative, the toner
density sensor 90 can be employed to detect the fluidity of
developer agitated and conveyed by the first and second conveying
screws 53 and 54.
The above-described embodiments show the developing device 8, the
detecting mechanism, the detecting methods of deterioration of
developer, the image forming apparatus 100, and the image forming
method, but the present invention is not limited to such methods,
devices, and apparatuses, except when specified in the
above-described embodiments.
For example, the detection method of deterioration of developer may
use at least one of the toner density sensor 90, the developer
amount sensor 88, the torque sensor, the image density sensor 18,
and the toner scattering sensor 89.
The above-described embodiments are illustrative, and numerous
additional modifications and variations are possible in light of
the above teachings. For example, elements and/or features of
different illustrative and exemplary embodiments herein may be
combined with each other and/or substituted for each other within
the scope of this disclosure and appended claims. It is therefore
to be understood that within the scope of the appended claims, the
disclosure of this patent specification may be practiced otherwise
than as specifically described herein.
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